The present invention relates generally to self-drilling threaded inserts. More particularly, it pertains to a threaded insert structure which when installed into a wall is adapted to receive a threaded fastener therein, where the threaded insert structure provides an anchor in drywall or sheetrock.
When objects or fixtures are to be mounted on a wall, the installer searches for a stud into which a screw or nail can be inserted. However, a stud is not always available or in a convenient place. Where an object is to be mounted in hollow wall construction such as plasterboard, sheetrock, fiberboard or any other material employed in hollow wall construction, the common practice is to use a hollow anchor for this purpose. The conventional hollow anchor is formed of metal such as zinc or of plastic such as PVC, which when hammered into a hole pre-drilled into the wall, is then adapted to receive a threaded fastener or mounting screw that goes through the mounting hole in the object and turns into the hollow of the anchor.
The installation of a conventional anchor entails three distinct operations: 1) drilling a hole, 2) hammering the anchor into the hole, and 3) inserting a threaded fastener into the anchor. The first and most critical step is the drilling of a hole in the wall which must be appropriate to that of the anchor. Should an oversize hole be drilled, then in the next step when the anchor is hammered into the hole, the anchor will not wedge firmly therein. As a consequence, it will not be possible to carry out the third step. In the third step, a threaded fastener is inserted into the hollow portion of the anchor. But if the anchor is loose in the wall hole, this will cause the anchor to turn as the fastener is turned, and the fastener will not be able to thread its way into the anchor.
The installation of a convention hollow anchor typically requires several tools including a drill provided with a drill bit having a diameter appropriate to that of the anchor, a hammer to drive the anchor in the hole drilled in the wall, and a screwdriver to turn the threaded fastener into the anchor or to later remove it from the anchor.
Though hollow wall anchors are used on a large scale by installers, the need to drill holes and then hammer the anchors into the holes is a practical drawback, for these operations are time consuming and impose distinct limits on the number of anchors that can be installed in a given period. In addition, if anchors of different sizes must be installed, then the installer must change the drill bit when switching from one anchor size to another, which, consumes time and reduces the productivity of the installer. Furthermore, when a wall anchor is hammered into a wall, the rear surface of the wall board is often destroyed, thereby minimizing the anchor strength of the wall anchor.
One approach to the above is a self-threading anchor with spreadable distal leg portions joined by a frangible drill end portion described in U.S. Pat. No. 5,692,864 to Powell on Dec. 2, 1997. In the xe2x80x2864 Patent, Powell teaches a spade-shaped drill end portion with a frangible web portion which holds the drill end portion together during drilling while allowing the drill end portion to split apart to accommodate the spreading of the leg portions. Other self drilling and self tapping anchors are described in U.S. Pat. No. 5,536,121 to McSherry on Jul. 16, 1996. However, the cutting portions of these anchors create rough cutting surfaces which decrease the strength of the engagement of any external threads. In addition, the rough cutting creates an unsightly appearance after the anchor is installed.
Accordingly, what is needed is an improved anchor bolt which requires a minimum number of tools to install. What is further needed is an anchor bolt which is aesthetically pleasing once installed, and is not unduly disruptive to a mounting surface. What is also needed is an anchor bolt which is securely mounted within a wall for attaching objects thereto.
An improved self-drilling plastic anchor bolt is provided which is installable in a wall with a screwdriver. The anchor bolt is adapted to receive a threaded fastener that holds a fixture or other object against the wall, where the anchor bolt dispenses with the need for a drill, a hammer, or any tool other than a screwdriver to install the anchor bolt.
The self-tapping anchor bolt has a head with a through-hole opening for receiving a screwdriver. In one embodiment, the through-hole is adapted to receive a Phillips screwdriver. The head is coupled with a shank at a first end of the shank, where a second end of the shank is coupled with a drill portion. The shank has a longitudinal cavity therein which is adapted to receive a set screw. In addition, the shank includes points of weakness therethrough to accommodate expansion of a portion of the shank after insertion of the set screw. The points of weakness allow for a portion of the shank to deflect away proximate the head. In another embodiment, the points of weakness allow for a portion of the shank to deflect away from the bolt proximate an intermediate portion of the bolt.
An external helical thread on the shank portion is coiled about the external surface of the shank and extends between the head and the drill portion. The drill portion includes a cutting edge and at least one helical flute for carrying away the material during installation of the anchor bolt.
In another embodiment, the self-tapping anchor bolt has a head with a through-hole opening for receiving a screwdriver. The head is coupled with a shank at a first end of the shank portion, where a second end of the shank is coupled with a drill portion. The shank has a longitudinal cavity therein which is adapted to receive a set screw. The longitudinal cavity, in one embodiment, is tapered. In addition, the shank includes slits therethrough to accommodate expansion of the shank after insertion of the set screw. In one embodiment, the points of weakness comprise slits. At least one portion of the shank is adapted to expand outwardly and is separable from the shank proximate the head. The portion of the shank, when partially severed from the shank upon insertion of the set screw, secures the anchor bolt within the wall. In one embodiment, an external helical thread on the shank portion is coiled about the external surface of the shank portion and extends between the head and the drill portion. The external thread allows for the anchor bolt to engage with the mounting surface before the set screw is installed. In another embodiment, the drill portion includes a cutting edge and at least one helical flute for carrying away the material during installation of the anchor bolt.
To install the anchor bolt, first a sharpened point on the drill tip is used to pierce the mounting surface. A screwdriver is then used to drill the anchor bolt into the wall. After the anchor bolt is inserted into the wall such that the head abuts an outer surface of the wall, a mounting set screw is inserted into the longitudinal cavity of the shank portion. A screwdriver is then used to concurrently apply an axial force while rotating the mounting set screw. As the mounting set screw is further installed into the anchor bolt, the set screw places an outward force on the shank, to thereby separate at least one portion of the shank. The at least one portion of the shank expands away to engage firmly into the wall. As the portion of the shank is wedged radially outwardly from the shank portion, the anchor bolt is held firmly within the wall.
Since the anchor bolt can be fabricated from high strength material, the anchor bolt can be manufactured at a relatively low cost. The anchor bolt is held in the wall by the resistance of the external threads on the anchor bolt which engages with the wall, in addition to the engaging member which is radially spreadable upon insertion of the fastener into the anchor bolt to provide a secure device on or to which structure can be securely mounted.
These and other embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.